ath10k: Get rid of superfluous call to pci_disable_msi()

The documentation states that pci_enable_msi_block() returns the number of
requests 'could have been allocated', not 'could allocate'. IOW, MSIs are *not*
enabled if a positive value returned.

kvalo: add commit log based on Alexander's email

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>